Any bag that is 25 or more pounds (11.35 kgs) in weight is normally classed as a heavy duty or industrial size bag. This class bag enjoys tremendous packaging and shipping usage throughout the world. Nearly all or all of the industrial bags produced commercially prior to this invention have been based on a preformed or pre-made bag construction.
It would amount to very meaningful cost savings, however, if heavy duty bags could be produced on a fast in-line operation, based on a form, fill and seal concept. The prior art, however, has not provided the technical progress that is needed in order to make a sure and widespread transition from the preformed, to an in-line formed, filled, and sealed industrial bag.
Perhaps the most crucial problem, if viable technical progress is to be made, is the need for improved methods and apparatus for forming the bag seals or welds. Achieving good sealing results has been a past problem even as regards preformed plastic bags which require only a minimum of sealing after filling, the majority of the seals having been pre-made by the bag manufacturer under controllable, essentially stress free, ideal conditions. For example, in the March 1968 issue of Food Engineering, it is reported at page 116 that:
"Bag damage with the all-plastic bag was considerable due to failure of the heat-sealed closure. The closure would open in transit, and that would be that. This isn't a product that can be recoopered."
The welding of heavy duty form, fill, and seal industrial bags is understandably even more touchy, since the process does not have the benefit of ideal bag manufacturing conditions. There is not the luxury of being able to form and cure the seals or welds in a stress free environment. Moreover, the fresh welds must accept the stress and distortions of the product load almost immediately, and must be formed with extremely high repeatability and good results for commercial acceptance. Still further, the welding technique must be able to securely weld through heavy gusseted areas if it is to achieve true success. A gusseted bag is relatively square and provides a stable pallet load, and it is essential that an industrial bag have this quality if it is to be an optimum bag. For illustrative example, a bag of 10 mil wall thickness would be 40 mils thick in the gusseted areas, 30 mils thick along the overlap or longitudinal seal, and 20 mils thick in other areas. The welding technique must accommodate such wide variances in thickness along a single weld line. Particularly, it must form a tough even weld at the points of abrupt thickness change, and without causing delineated lines of pronounced weakness or thinning.
The method and apparatus for properly side gusseting the formed, filled and sealed industrial bags is another problem area. For example, in a form, fill and seal process, the side gussets must be formed after the bag has been influenced by the distortion and weight of the product load, whereas, in a preformed bag, the side gussets can be neatly tucked in and secured under far more compatible conditions. Particularly if a form, fill, and seal industrial bag is to be optimally suited for commercial use, i.e., palletizing, there must be provisions for including functionally adequate side gussets in the ultimate bag structure.
Still further, the desired method and apparatus for producing an acceptable form, fill and seal industrial bag, should advantageously provide for flexibility in the materials from which the bag can be formed. The ultimate performance of an industrial bag, of course, depends on the materials from which it is manufactured. It is extremely desirable, for example, that in some uses, the industrial bag be provided with multiple plies of material to better absorb the expected handling abuses. Most desirably, therefore, the operation should be sufficiently flexible to permit the usage of webs of multiple plies of material, together with tough scrim layers such as of fabric, nylon, rayon, and the like, that give the bag improved overall integrity. A multi-layer bag is generally felt to be tougher than a single ply bag of equivalent thickness, and the scrim layers can add considerable abuse resistance to the bag.
As yet another factor to be dealt with, a prospective form, fill, and seal method and apparatus for industrial bags should, for optimum versatility, expediently prepare the bag for a post-shrinkage step. This flexibility will permit the bag to be tightly shrunk about the product so that it retains a firm, tight character through a normal or even extended use period.
Accordingly, it is the primary objective of this invention to provide an apparatus and method suitable for in-line forming, filling, and sealing of industrial size bags.
It is particularly among the objectives of this invention to accomplish the primary objective with a maximum of finesse and flexibility, whereby the method and apparatus are advantageously designed to:
i. form exceedingly tough welds with a very high degree of repeatability, that can withstand the abuses of commercial handling with an acceptably low frequency of failure, and, that can withstand the weight of the product load with sufficient immediacy to enable fast production rates;
ii. permit manufacture of side gusseted bags with optimum palletizing and handling characteristics, and wherein the welding procedure is able to weld through and secure the gussets strongly in the bag structure;
iii. handle excessively dusty products of the type that normally give problems through contamination of welding surfaces;
iv. optimize the palletizing and handling characteristics of the bag and minimize material usage, by forming a tight, firm bag about the product;
v. automatically precondition the bag for a post-shrinkage step;
vi. achieve finesse in holding and maintaining proper registration so that the bags can be produced with accurate registration of printed blocks and indicia thereon; and
vii. fill the bags in a manner that complements the welding and gusseting of the bag with repeatedly good results, and that facilitates the performance of these objectives at commercially acceptable manufacturing speeds.